This invention relates generally to fiber optic cables and, more particularly, to apparatus for terminating plastic fibers in such cables.
Originally, glass was the sole material used as optical fibers. Recently, plastic optical fibers have gained widespread acceptance, especially for use in data transmission. Optical fibers used for data transmission are supplied in cable form in which the cable comprises a pair of plastic fiber cores, each with a thin cladding, and a protective jacket which can include strengthening members. Connecting the fiber optic cable to another device, such as an electro/optic device or another cable, requires the formation of a terminal on the cable. The termination of the cable is often performed as a field operation, such as when installing data transmission systems, such as computer LANs (Local Area Networks). The terminal installer normally encounters the ends of fiber optic cables extending from the wall of an office.
To provide an optically efficient interface between an optical fiber and another device, it is necessary to mount the optical fiber ends in a suitable terminal fitting in a manner that will provide good signal transmission across the interface. This requires that the optical fibers have a flat, smooth end surface. Two methods of forming this end surface during termination are in general usage.
In one, the "polishing" method, the cable jacket is stripped and the clad fiber is epoxied into an end fitting, such as a ferrule or a multiple fiber connector. The fiber end is snipped off to form a generally flat surface near the terminal face of the end fitting. This surface is then polished to a predetermined degree of smoothness to eliminate pits which adversely affect light transmission. This polishing method is a laborious, exacting and, thus costly, process which requires repeated visual inspection to determine when the predetermined degree of smoothness is achieved.
The other "hot plate" method involves stripping the cable jacket, inserting the fiber into an end fitting and projecting it through the exit aperture beyond the terminal face of the fitting. The fiber end is then snipped off a predetermined short distance beyond the terminal face. The fiber ends are brought into contact with a smooth plate, which is then heated to melt the fiber ends. Heat is then removed from the plate, which begins cooling. When plate has cooled sufficiently to solidify the fiber ends, they are removed from the plate. This "hot plate" method leaves the fiber end with the same smooth, flat surface as the plate.
Both of the termination methods described are time consuming and inefficient and utilize apparatus that is awkward to use in the field. The polishing method requires that the terminal installer determine when a sufficiently smooth polished end surface has been attained and requires repeated inspection. The hot plate method requires close attention by the operator who must judge when to remove heat. Otherwise the fibers will be overheated, and begin melting beyond their terminal faces, causing fiber distortion which will severely degrade light transmission. The hot plate method also requires judgment as to fiber perpendicularity to the plate surface and as to when the plate has cooled sufficiently to enable removal of the fiber from the plate.
Thus there is a need for apparatus that can be utilized in the field to reliably terminate a plastic optical fiber with a flat, smooth end surface.
There is a further need for such apparatus that is portable and easy to use.
There is a yet further need for such apparatus that minimizes the need for human judgment, while providing a reliably flat, smooth plastic optical fiber end surface.